Problem: $10st - 2su + 4s - 3 = 9t + 5$ Solve for $s$.
Combine constant terms on the right. $10st - 2su + 4s - {3} = 9t + {5}$ $10st - 2su + 4s = 9t + {8}$ Notice that all the terms on the left-hand side of the equation have $s$ in them. $10{s}t - 2{s}u + 4{s} = 9t + 8$ Factor out the $s$ ${s} \cdot \left( 10t - 2u + 4 \right) = 9t + 8$ Isolate the $s$ $s \cdot \left( {10t - 2u + 4} \right) = 9t + 8$ $s = \dfrac{ 9t + 8 }{ {10t - 2u + 4} }$